The present invention relates generally to the hydraulic operation of vehicle friction clutches, and more specifically to a hydraulic piston/cylinder unit for use in a clutch operating system.
Clutch release systems having a slave cylinder as the central release member are known. They comprise a slave cylinder concentrically enclosing a drive shaft and formed as a piston cylinder unit. The cylinder can be detachably fixed on a gearbox housing. The piston can be a ring piston which is displaceable in a circular ring shaped pressure chamber of the cylinder, and the piston can be associated on the pressure chamber side with a seal which is fastened by a seal carrier on the ring piston and is held in positive engagement in the seal carrier.
The invention also relates to a hydraulic piston/cylinder unit, which may be a slave cylinder for a hydraulic release system of a motor vehicle friction clutch (or may be a piston/cylinder unit for some other application). The cylinder pressure housing can have a circular ring shaped pressure chamber with a ring piston displaceably guided in the chamber and an elastic seal fixed with keyed engagement on the ring piston by means of a seal carrier.
The invention further relates to a hydraulic work cylinder which is preferably formed as a component part of a release system for a shift and separate clutch and may be mounted in a vehicle between an internal combustion engine and a manual shift transmission. The release system can comprise a master cylinder unit operated by means of a pedal or an automatic release unit and a pressure transfer mechanism to a further cylinder, which is also to be called a slave cylinder, which concentrically surrounds a drive shaft which connects the internal combustion engine to the transmission. The cylinder forms a pressure chamber which seen in cross-section is circular ring shaped and in which a ring piston is guided axially displaceable between a bore wall of the cylinder and a guide sleeve concentric therewith. On the pressure chamber side the ring piston is associated with a seal.
A release system with the construction explained above is known from DE 196 09 472 A1. The known release system is fitted with a seal carrier which is made without stock removal from steel. This support has on its radially outer projection spaced from the free end a locking nose which in the installation position engages with keyed engagement into a ring groove or local recess of the piston. The locking nose which is shaped semi-circular allows an automatic snap-fit engagement which can become loose by itself e.g. in the event of unfavourable manufacturing tolerances or ill-matched pairings. A seal carrier separated from the ring piston leads to a breakdown or function failure of the slave cylinder. The internal profiled section of the seal carrier which serves to house and fasten the seal has according to the known release system a relatively large axial extension which has a direct detrimental effect on the guide length of the ring piston.
From the French Patent Application FR 2 730 532 on this subject a slave cylinder is known, more particularly for a hydraulic release system of a friction clutch of motor vehicles wherein for the positive locking connection of the seal on the ring piston a retaining plate is provided which is hooked by its ring-shaped part on the outer circumference of the ring piston by means of claws engaging in corresponding recesses and is anchored at the end side in the seal by a radially inwardly directed area. Through this type of fastening a secure hold of the seal on the retaining plate is not guaranteed since the remaining cross-sectional area of the sealing material is now only small and can easily wear away. Furthermore the radial area of the retaining plate engages only from the outside on the seal so that it is easy for the seal to cant.
From DE 34 39 652 A1 a slave cylinder is known for a hydraulic release system of a friction clutch of motor vehicles wherein a stripper element is provided between the ring piston and seal and engages from inside and outside round the seal in dovetailed fashion and thus produces a fixed connection with the seal whereby the stripper element only adjoins the ring piston loose and the problem thereby exists that the contact between the ring piston and stripper element can be lost which leads to function failures of the slave cylinder. Play between the support faces of the seal and the sealing ring support reduces the stiffness and thus degree of efficiency of the operating system associated therewith.
Furthermore from EP 0 168 932 A1 a hydraulic release device is known having a further release shoulder. In order to obtain a surface which favours the wear behaviour of the sealing lips of the ring piston seal the guide faces on the bore wall of the cylinder and on the guide sleeve are subjected to a special mechanical finishing treatment. By way of example the guide faces, i.e. the seal tracks can be enhanced by grinding and/or polishing or honing. These processes extend the manufacturing cycles of the cylinder and are thus disadvantageous from the cost point of view.
For a specific surface treatment of the seal tracks it is generally known to subject these to a sand-blasting treatment in order to improve the wear and/or sliding properties of the seal. By way of example the seal track can be enhanced in an aluminium cylinder by sand-blasting with glass balls. However such a process is very expensive and incurs high costs.
Coating a sealing element can be concluded from DE 40 35 657 A1. To this end in order to influence the sliding ability a foundation body of elastomer can be coated with a material substance. By way of example polyvinyl chloride is used for the coating which is applied onto the foundation body but does not however project into the marginal zone of the foundation body. Such a process is very expensive and demands high production quality. Manufacturing the foundation body and applying the coating must thereby be carried out so that a definite wall thickness of the sealing lips is set in order to obtain for example the elasticity required for the sealing action.
The object of the present invention is therefore to provide a seal carrier which:
ensures an effective permanent fixing on the ring piston;
allows improved support of the seal;
reduces the axial structural length.
The object of the invention is to avoid the faults of the known solutions and to provide a slave cylinder whose sealing assembly ensures precision guidance of the seal in the pressure chamber and furthermore guarantees a permanent fixed connection of the seal relative to the ring piston. Furthermore the seal carrier is to be capable of reliable mass production and able to meet the demands regarding strength whilst taking up minimal axial structural space.
Starting from the technical faults of known solutions it is furthermore the object of the invention to provide a seal for a hydraulic release device
which is optimised with regard to wear
whose service life is improved
whose friction is reduced and
which cuts down on noise.
Furthermore the release device is to be capable of economic production.
In a hydraulically operable release system of the kind in which a seal is secured on a ring piston by a circular, ring-shaped seal carrier, the object of the invention is achieved by providing the seal with an undercut section that fits snugly into the seal carrier without forming any gaps.
An advantageous embodiment has a seal carrier with different wall thicknesses. Starting from the greatest wall thickness in the area of the outer axial projection according to the invention the wall thickness is provided with a reduced thickness in other sections of the seal carrier, more particularly in partial areas of the internal profiled section or opening directed towards the seal. The proposed difference in wall thicknesses takes into account the manufacturing process, i.e., the deep-drawing process which is preferably used allows the seal carrier to be designed with the optimum profile determined for example by FE-calculation (finite elements). At the same time the seal carrier according to the invention allows optimum axial structural length and shaping which ensures a cost-effective production.
The invention furthermore includes an enlarged end face of the seal carrier on the seal side. To this end the rounded transition between the end face and the inner or outer axial projection of the seal carrier is designed so that the sections of the end faces or the axial projections intersect as a secant the curve formed by the radii at the transitions. This geometric design of the seal carrier enlarges the support face for the seal which has an advantageous effect on the service life of the sealing ring. According to the invention in each rounded transition zone between the end face and the axial projection of the seal carrier it is proposed that starting from the end face an at first smaller radius is adjoined by a larger radius. This measurement increases each time the end face and allows a more heavily rounded end-side transition to the sleeve face of the axially aligned projections of the seal carrier. A seal carrier formed in this way avoids or reduces a gap extrusion of the sealing material between the seal carrier and seal track. At the same time the shear tension in the seal is reduced in the area of the support on the end sides of the seal carrier.
A flanged section provided at the free end of the outer axial projection serves to fasten the seal carrier. In the installation position of the seal carrier the flanged section is angled inwards to produce a radial overlap with a sleeve structure of the ring piston. The flanging can thereby provided round the entire circumference or partially.
A definite overlap in the area of the undercut sections is provided for the internal profiled section of the seal carrier according to the invention provided for fastening the seal. A measurement Hxe2x89xa70.1S1 is provided for the at least one-sided radial overlap. This overlap makes it possible when installing the seal for the sealing material to fill out the internal profiled section of the seal carrier at least substantially and thus for the seal to receive a permanent hold.
One advantageous development of the invention provides a ring piston which is provided on the pressure chamber side with a shoulder protruding axially from the end side. This shoulder on the inside advantageously increases the guide length of the ring piston on the guide sleeve. The shoulder is thereby formed so that this contacts the seal carrier neither radially nor axially.
To achieve the optimum axial structural length of the seal carrier according to the invention a spacing measurement L1 is determined between the end side and the planar surface of the seal carrier which corresponds to  greater than 3.5 times the value of the wall thickness S1. Seal carriers with small spacing measurements defined in this way allow a desired extended axial guide length of the ring piston which has an advantageous effect on the function of the slave cylinder.
An advantageous development of the invention proposes designing the seal carrier so that a doubled or folded area adjoins the lead-in zones of the opening. As a spacing measurement for a seal carrier designed in this way a measurement is provided between the end side and the planar surface of the seal carrier which corresponds maximum to 3.5 times the value of the wall thickness S1. A seal carrier with a doubled area previously explained consequently allows the axial structural length of the seal carrier to be further reduced.
For the wall thickness S1 of the seal carrier in the outer axial projection a measurement of greater than 0.2 mm has proved practical and expedient. A seal carrier with this wall thickness allows a cost-effective production which can be made without stock removal and nevertheless has sufficient strength.
The configuration of the seal carrier according to the invention furthermore includes an internal profiled section mounted centrally in the circular ring shaped end face of the seal carrier. This internal profiling ensures in the case of a seal biased with pressure that the axial force introduced from the seal onto the seal carrier is transferred in a straight line to the ring piston. For groove ring seals used having asymmetrically arranged sealing lips the invention likewise includes a seal carrier whose axis of symmetry (Sa) from the internal profile for holding the seal is arranged coinciding with or off-set from the end-side centre (M) of the seal carrier.
In the rounded transition zone between the end face and at least one axial projection of the seal carrier it is proposed according to the invention that starting from the end face an at first smaller radius is adjoined by a larger radius. This measurement enlarges each time the end face and allows a more heavily rounded end-side transition to the sleeve face of the axially aligned projections of the seal carrier whereby a desired smaller edge radius is set which reduces a gap extrusion of the sealing material.
A further advantageous design of the invention provides a seal carrier having a symmetrically shaped internal profile which has two undercut sections. Deviating from this the invention likewise includes sealing supports with only one undercut section which can be aligned in the direction of the outer projection or towards the inner projection. The invention further includes undercut sections of different geometric shape in an internal profile which can be determined for example in dependence on the material pairing of the seal carrier and/or seal or on other parameters.
The seal carrier according to the invention having multi-curved shaping is provided in the individual transitions with differently shaped radii. Fixing the radii in this way serves on the one hand to enlarge the end-side support surface of the seal on the seal carrier and to facilitate the elastic deformation of the sealing substance for fitting into the opening or internal profiled section of the seal carrier and on the other to simplify the manufacture of the seal carrier. In the area of the lead-in zone of the seal carrier the radii thereby exceed the measurement of the wall thickness S1. The inner radii in the internal profiled section or mounting of the seal carrier are xe2x89xa6 the radii at the lead-in zone.
The idea of the invention furthermore includes an overall length of the outer axial projection which is greater than the distance measurement between the end side and the planar surface of the seal carrier. The axial projection can thereby be adapted to the relevant conditions or requirements relating to the shape of the ring piston and the type of fastening.
The idea of the invention provides a ventilation groove in the seal carrier for the purpose of improving the seal assembly. The air included in the internal profiled section can escape through the seal groove when mounting the seal and thus the internal profiled section can be completely filled out with sealant material. A ventilation groove is thereby preferably provided which is formed axially parallel to the outer projection in a protrusion of the seal carrier. Alternatively the seal carrier can be provided for ventilation with a bore which is preferably formed in the planar surface.
A further development of the seal carrier provides that the inner projection is guided up to the end face of the ring piston whilst maintaining an annular gap. For ring pistons which are provided on the end side with an axially protruding shoulder by which the guide length of the ring piston on the guide sleeve can be increased, the inner projection of the seal carrier is correspondingly shortened so that an annular gap is likewise set between the shoulder of the ring piston and the projection. For further optimising the guide length of the ring piston its axially protruding shoulder can be guided up to the radially aligned section of the seal carrier. The inner projection of the seal carrier is thereby omitted. To avoid contact or support of the seal carrier on the shoulder of the ring piston an axially and radially setting annular gap is provided between these component parts.
For the inner projection of the seal carrier the invention proposes that this runs conical at least in part. Starting from the end side of the seal carrier towards the free end, the inner projection is directed radially outwards. This design prevents detrimental contact of the guide sleeve by the free end of the projection. The design of the inner projection according to the invention further proposes that in the installed state the projection is guided up to the end side of the ring piston whilst maintaining an annular gap. The annular gap for which a measurement of xe2x89xa70.1S1 is preferably provided creates a controlled seal carrier which is supported on the ring piston solely through the planar surface.
According to the invention a metal material capable of being deep drawn is provided as the material for the seal carrier which is made without stock removal. A steel plate St4 or a comparable material is a suitable example.
The object of the invention is further achieved in that the seal carrier has a circular ring shaped mounting chamber opening towards the seal and provided with an inner ring and outer sleeve, that the inner space in the end area of the mounting chamber facing the seal is reduced, that the seal has at least a correspondingly shaped recess, ring groove or the like for keyed connection with the seal carrier and that the seal carrier is constructed of two component parts which can be made separately from each other. It is thereby ensured on the one hand that the seal is fixedly anchored in the seal carrier and is enclosed by the inner ring and/or outer sleeve of the circular ring shaped mounting chamber wherein the seal is not weakened in cross-section to the extent that it can rip or tear. The invention reduces the axial and radial play between the sealing ring and sealing ring support and at the same time improves the stiffness and degree of efficiency of the overall system. In that the seal carrier consists of two parts these individual parts can on the other hand be easily manufactured so that overall a cost-effective seal carrier is produced.
The reduction in the internal spacing in the end area can be formed both by a restriction on the outer sleeve and a widening of the diameter on the inner ring whereby both measures can also exist. In order to avoid sharp edge transitions in the case of the restriction or diameter expansion these are provided in the form of ring beads. Corresponding deformations on the seal also produce suitably rounded transitions there.
The two-part construction of the ring support is preferably designed so that the outer sleeve is formed circular ring shaped and that inside same is the inner ring which is adjoined on the side remote from the seal by a disc-like flange which is in active connection with the outer sleeve.
This active connection can be made on the one hand so that the disc like flange is fixed in a fixing groove on the inner circumference of the outer sleeve. This is particularly advantageous when the outer sleeve and inner ring are made of a material having sufficient elastic deformability whereby then the disc-like flange is pressed into the outer sleeve and snap-fits in the fixing groove. Various materials can be used such as for example steel, aluminium, sintered parts or plastics parts whereby the latter can also be strengthened by steel reinforcements.
The disc-like flange can also have on its outer circumference projections which project into windows or recesses on the outer sleeve. Also with this design the disc-like flange can be pressed into the outer sleeve whereby the projections snap-fit in the windows or recesses on the outer sleeve.
In a further development of the invention the disc-like flange can also be fixed in one direction on one or more stops on the inside face of the outer sleeve and can be fixed on the opposite side by material embossing or welding. The disc-like flange can thereby also be stuck to the outer sleeve. With plastics parts fixing the disc-like flange can be achieved by ultrasound welding whereby in the case of metal parts laser welding or soldering in a continuous furnace can also be used. Both the outer sleeve and the inner ring can if they are made of aluminium or steel also be formed as flow pressed parts. The or each stop can be produced by rolling or embossing, particularly if the outer sleeve is made of steel, whereby the disc like flange can also be connected non-detachable to the stops directly e.g. through spot welding or through resistance welding.
The disc like flange can be fixed on the outer sleeve according to a further design of the invention where after installing same the outer sleeve receives grooves, projections, studs or the like by rolling or imprinting each side of the disc like flange.
Also the disc like flange can be fixed by one or more stops, by projections, studs and the like on the inner circumference of the outer sleeve on one side and by the end face of the ring piston on the other since the outer sleeve clamps the disc-like flange along with same through its keyed fastening on the ring piston.
The disc like flange can finally be provided on its outer circumference with a thread and can be screwed onto a counter thread on the inner circumference of the outer sleeve.
The outer sleeve in turn has at its end area remote from the seal inwardly directed projections, studs or the like which can hook with keyed engagement into corresponding recesses, undercut sections or a ring-shaped restriction on the ring piston.
A further alternative fastening of the inner ring on the outer sleeve is provided in that the disc like flange has on its outer circumference a substantially cylindrical extension which extends in the direction remote from the seal and corresponds with the inner circumference of the outer sleeve whereby the cylindrical extension is fixed on the inner circumference of the outer sleeve by adhesive, welding or press-fit. The cylindrical extension can also have windows or openings which correspond with the inwardly directed projections on the outer sleeve so that these undertake both the fixing of the cylindrical extension whilst ensuring the fastening on the outer circumference of the ring piston.
The problem previously mentioned is further solved according to the invention by a seal which is subjected at least in part to chemical finishing. Particularly suitable for this are halogens though which a marginal zone of the sealing substance can be chemically changed. Halogens are characterised by a large reaction capacity which can be transferred to materials from which seals are made.
Advantageously by a chemical halogen treatment of the seal it is possible to achieve a purposeful hardening or brittleness of a marginal zone of the seal. The chemical treatment which is also termed halogenization signifies the introduction of halogen into an organic compound for example into a benzene ring. The bearing proportion of the sealing lips can be directly influenced by the changed material properties for example. By including the special material properties of the relevant sealing material used each time and taking into account the different reactions it is possible to change or influence by different parameters the depth of penetration of the marginal zone of the seal. As a result of the chemical treatment according to the invention which influences the bearing proportion of the sealing lips, on the one hand the sealing quality of the seal is improved and on the other the sealing lip becomes more resistant to wear as a result of the brittle finish or surface hardening. Furthermore the chemical treatment reduces the friction force so that the release force required to operate the shift and separate clutch is clearly reduced independently of the temperature of the release system. Finally the seal according to the invention reduces the noise development as a result of clear friction conditions. As a result of the brittle condition the disadvantageous stick-slip effect which is linked with a corresponding noise development is now avoided. The effect also designated back-slipping leads in short intervals periodically to sticking, breaking loose and further movement of the sealing lip on the sealing track face.
Advantageously through the invention the micro deformation of the sealing material in the area of the sealing lip is reduced whereby the friction can be directly reduced. The chemical finishing treatment in conjunction with the optimized geometry of the seal leads to a solution to the problem on which this invention is based. As a result of the changed shaping a reduced contact length of the seal is set and thus a shortened dynamic cylindrical contact surface of the sealing lips in order to minimize the friction. The optimized sealing geometry according to the invention creates overall a shortened seal which allows an increased stroke of the ring piston or optimisation of the structural space in the axial direction of the cylinder.
As a cost-improving measure the invention proposes restricting the chemical finishing treatment to the sealing lips of the seal. To this end a fluid is preferably used in which halogens are dissolved. Deliberately immersing the seal can consequently result in a local chemical change of the marginal zone. The hardening or brittle nature desired for the sealing lip is thus not transferred to the remaining areas of the seal.
In a further development of the invention it is proposed for the chemical finishing treatment to chlorinate, brominate, iodinate or fluorinate the seal or partial areas of the seal. This finishing treatment can also be carried out in a gaseous or liquid phase and is likewise suitable for the materials normally used for seals, such as e.g. EPDM. Processes normally used in the chemical industry are used for this purpose. With a fluorinated sealing lip an effect is set wherein the sealing lip remains relatively elastic and has a sufficient sealing action from fluids but allows gas to pass through the sealing lip to a limited amount. Chlorination is used in particular to achieve a relative stiffening of the sealing lip but here a reduced sealing friction is set compared with a fluorinated sealing lip.
The chemical finishing treatment changes the marginal zone in that for example chlorine or another halogen diffuses into the sealing substance and thereby influences the marginal zone to a depth of  greater than 5 xcexcm.
For the hydraulic release device different pairings of material are provided between the seal, i.e. the sealing lips thereof and the seal tracks on the bore wall of the cylinder and guide sleeve. Preferably an elastomer such as EPDM, HNBR, NBR, is provided as the sealing material. A metal material, more particularly aluminium is provided as a suitable material for the cylinder. The guide sleeve which is integrated in the cylinder represents however a sheet metal part which is made without stock removal by the deep-drawing process.
A bearing proportion of  greater than 15% is provided for the surface quality of the sealing track on the bore wall of the cylinder. The sleeve face of the guide sleeve on which the inner sealing lip of the seal sealingly adjoins has however a bearing proportion of  greater than 20%.
The structure of the release system according to the invention furthermore has an asymmetrically shaped seal with sealing lips whose longitudinal extension and wall thickness differ from each other. The inner sealing lip has a greater length extension than the outer sealing lip. On the other hand the wall thickness of the outer sealing lip exceeds the wall thickness of the inner sealing lip.
For an optimum design of the seal a wall thickness ratio of the outer sealing lip to the inner sealing lip of             L      6              L      5        ≥  1.1
has proved advantageous. For the longitudinal extension of the sealing lips a length ratio             L      1              L      3        ≥  1.1
between the inner sealing lip to outer sealing lip has proved optimum.
The further development of the seal comprises a V-shaped ring groove on the end side restricted radially by the sealing lips. The groove depth is thereby defined by a measurement which extends from the back of the seal to the groove base. According to the invention it is established that this measurement always exceeds a length measurement from the back of the seal to a function point of the inner sealing lip.
The device of the seal according to the invention further includes the shaping of an outer contour of the inner and outer sealing lip. According to this each sealing lip in the non-installed state intersects an active line corresponding to the sealing lip track face in the installation position on the bore wall of the cylinder or on the sleeve face of the guide sleeve. Starting from the back of the seal the outer contour of the two sealing lips defines on the inside an underlap zone B;D extending up to the active line. After the intersection of the sealing lip outer contour with the active line the outer contours of the two sealing lips define on the outside an overlap zone A;C. The overlap zones A;C thereby each extend from the intersection with the active line up to a function point at which each relevant sealing lip adjoins the sealing track with the greatest radial pretension.
The following surface area ratios can be designated optimum for each relevant sealing lip. For the inner sealing lip a ratio of overlap zone A to underlap zone B is       A    B     greater than   0.5
and for the outer sealing lip a corresponding ratio is provided of       C    D     greater than       0.7    .  
As an alternative to the surface area ratios mentioned above the invention also includes a surface area ratio of       A    B    =  1
as well as a matching surface area ratio       C    D    =  1.
Furthermore the seal can have matching surface area ratios             A      B        =          C      D        ,
i.e. the surface areas of the overlap zones and underlap zones have the same size.
The design of the seal further includes a measurement ratio which is set between a vertical measurementxe2x80x94which determines the radial spacing between the active lines of the two sealing lipsxe2x80x94and a length measurement between the back of the seal and the free end of the radially inner sealing lip. This measurement ratio             L      1        +          L      4            D    1  
is to amount to  greater than 0.6.
In order to determine the length measurements of the two sealing lips, starting from the back of the seal to the function point, the following length measurements are provided: for the inner sealing lip a length measurement of  greater than 2.6 mm is provided, characterised by L1. The corresponding length measurement for the radially outer sealing lip, designated L3, amounts to  greater than 2.2 mm.
The two sealing lips each form, starting from the function point, an end section whose outer contour in the non-installed state runs at an angle of xc2x15xc2x0.
The depth of the V-shaped circumferential groove formed at the end side in the seal is determined by a measurement ratio which is related each time to the back of the seal. The measurement L1 between the back of the seal and the function point of the inner sealing lip set in relation to the measurement L2 between the groove base of the ring groove at the end and the back of the seal amounts to  greater than 1. This measurement ratio prevents the seal from becoming weakened in the area of the sealing lip root.
According to a further development of the invention each sealing lip is provided on the outer contour in the area of the function point with a radius R1; R2. Thus a rounded transition is set in the area of the function point between the substantially cylindrical end section and the outer contour of the seal running towards the back of the seal.
For the V-shaped ring groove of the seal according to the invention it is proposed that this forms a radius R3 at the groove base. The size of the radius R3 is thereby selected so that this exceeds the radius R1;R2.
The invention further proposes a rounded transition from the outer contour of the relevant sealing lip to the back of the seal. This transition is likewise designed in the form of a radius R4; R5 wherein these radii are larger than the radii R1; R2. The radii R4; R5 can be dimensioned both different from each other or the same size.
For the partial chemical finishing treatment of the seal it is proposed that each relevant sealing lip is biased in the area of the outer contour each time starting from the tangent point of the radius R4; R5 to the back of the seal up to the free end.
The chemical finishing treatment of a sealing substance according to the invention can be used quite generally for seals in vehicle hydraulics. Both seals which are used in a master cylinder and seals for a master cylinder can be subjected to a halogen treatment where necessary.